Just my experience: I don't use anything special, just 'my' gritty mix & they seem to like it...

Semps in photos I posted are not fertilized...

I apologize Rina, I was just trying to respond more to the part of the original post where they said something like, "the growth was not abundant without regular synthetic fertilizer." The semps you posted are gorgeous and look rather abundant to me. Do they get any kind of fert or just whatever they get from the rain?

I'm personally not in any hurry for my semps to get huge and have them in just the traditional gritty mix as well. I just let them get rained on and have dumped the rest of what I have in the odd watering can on them as I pass by occasionally but that's about it. Certainly not a regular fertilizing regimen by any means.

I have been growing semps my entire gardening life, both in containers and in the ground. IME, they are not the slightest bit fussy about soils other than they must be well draining. They have a very shallow root system and can thrive in very poor soils as well as more organically enriched soils but I have never seen them demonstrate a clear preference :-) It just needs to be fast draining, whatever it is.

I have also never consciously fertilized them. They do not require it and it can lead to too rapid and less durable growth.

The soil do need fertilizer but it can not necesserily be the conventional soil. Home made ertilizers are also good.

John

No need to apologize! I just wanted to say what I do - & I don't fertilize them. Pots are outside & get 'watered' when it rains. They all sarted as a very small clumps: below is the photo of just 1pot of Oddity I originaly purchased:

That was in fall of 2016, & now I have literally hundreds of them (besides number of plants I gave away). I have them in round bowls, plastic tubs, plastic pots...It is probably 2-3 hundred of plants now, maybe more.

Golden nugget was purchased in spring 2021, & it was just 1bigger rosette + 2 chicks. The photo posted was taken in Oct. 2021, & shows more chicks as they grew.

Those Golden nuggets are in pots only (smaller # of the plants; 1 smaller pot with just 2 plants to the right); but many grow in ground same way. As gardengal sayz, as long as they have good drainage. I find them very undemanding.

Here is another one I also purchased in spring of 2021 it was just 1pot (Citrus Sunrise). I divided the chicks & potted 1-2/pot. Photo shown was taken also in Oct; they grew well. There are at least 3 more pots (under the snow now, so can't count them)

@rina_Ontario,Canada 5a What is your formula for gritty mix, and what are the particle sizes of each component? That second photo in your first post definitely looks abundant and I am not understanding how that growth is possible in the gritty mix with no fertilizer.

westes

'My' gritty mix is one I use for all my succulents. Approx. equal amounts of sifted perlite and #2 chicken grit + small amount (approx. 25-35%) of soil or cococoir, whatever I have handy. I believe that mix in the photo of pots with Citrus Sunrise (post just before this one) has less grit since I wasn't able to get #2. Particles are about 3-5mm; that is the grit #2 (growers size). I sift perlite to about he same size. I really don't use fertilizer - probably I should; I would use leftover water with fertilizer after watering the vegetable garden - but that is almost never. I use rain & rain water to water my plants. The mix dries up fast. That Oddity (photo you mentioned) really grows very well. I have many, many containers of it. Here are just few of the pots: (you can see I use a lot of topdressing; size of gravel is one size bigger than what I use for the mix)

But all the semps grows the same, in containers or ground:

@rina_Ontario,Canada 5a When I say "gritty mix" I mean Tapla's formula for *the* "Gritty Mix": 1/3 sized bark, 1/3 turface, 1/3 sized grit. You do not have the Turface, but what is interesting is that you said 25% to 35% *soil*. What soil is that? Ontario soil? Ontario soil goes from between sandy loam and silt loam to clay loam.

westes

I stopped making 'classic Tapla's gritty' because I couldn't get appropriate bark (there is reptibark that is suitable, but too expensive for amount I needed). I have turface (still have 1 more 25lb unopened bag), but found it too water retaining in that amount (1/3rd) . I may throw a handfull into the mix, but seldom & didn't even mentioned it because of that. Instead, I use bit of soil. To me, either could be used in appropriate amounts. You don't have to use his receipt exactly - even he say so. Use it as a guide, experiment, use what is available to you. Just make sure your mix is fast draining...

In pots, I use just regular potting soil sold anywhere, or cococoir. I actually often use even less than 25-35%. I have many pots that I used only mix of perlite & grit. I used this as experiment, but it worked & plants are still in it. The ground soil here is very much heavy clay, & I make sure there are rocks that elevate planting levels, & I also make mounds to improve drainage.

I have sempervivum growing on rocks and boards w/o the benefit of soil.

It's interesting that the plants growing w/o soil are often less than 1/10 the size of the plants that tumble off the rocks/ board and take root in the ground.

Al

Rina,

Although there are many factors to consider, does the potting soil you use come pre-fertilized? Miracle-gro and many other brands typically do.

Al,

I think this kind of drives the point home that the plants will grow as large or as quickly as the ambient nutrient levels allow them to, right?

Westes,

I still generally stick by my point of it's not the substrate that matters as much as there is some sort of way nutrients are available to the plants. Clay has a very high CEC and is thus usually very good at holding on to nutrients. (Please note, I'm not a biologist/horitculturalist/botanist so this is my rough understanding of how things work.) So while the plants may seem to have a strong preference for clay loam, it still boils down to the fact that the actual preference they have is for a substrate that provides the nutrients they need to grow robustly.

"Al, I think this kind of drives the point home that the plants will grow as large or as quickly as the ambient nutrient levels allow them to, right?" That's true, but when they are growing on rocks and boards with no soil to hold moisture, water availability is also a very significant limiting factor when it comes to their size.

Al

John

I don't look for any 'special' soils, & try not to buy MG if there is another brand available. And I re-use lots of soil - as long as it wasn't full of bugs...

In my experience, Sempervivum arachnoideum are naturally quite small, typically about 1' - smaller than many other var. The 'bigger' ones in the photo (arachnoides) are only taller because they are going to bloom...

Heavy clay doesn't provide very good drainage, that is why I use rocks & stones & plant on mounds. That is the reason I keep many plants in the pots too...

I suspect that clay loam as even 10% of the soil mix would be adequate to satisfy whatever need Sempervivum seems to have for that substrate. John, of course, this is about how clay holds and delivers minerals to the plant. That would be the obvious hypothesis.

I... yeah Westes, your obvious hypothesis was obvious and we've largely agreed with you.

What I'm pointing out is that it's not the "clay" or the "loam" that semps need. Your answer, while not incorrect, could be developed further. You're tunneling on the materials when the point (in my opinion) is about showing that it's about the properties. Clay loam is just fine particulate matter that has a relatively high CEC and a combination of organic and inorganic materials.

You don't need clay loam specifically. You can use whatever material you want that fits the bill of providing nutrients to the plant. If you don't want to use a synthetic liquid fert, you can just as easily use osmocote or something and still achieve the same effect without any clay loam.

@John (Zone 5b/6a, IN) Probably the issue is the CEC but might also be about how the plant's roots respond to a particular substrate. Outside of a research environment, no one is going to figure that out. I have tried compost and I have tried Osmocote, and neither has the same effect for this specific genus.

For the most part, the medium isn't likely to be a key to their viability/survival. They will tolerate any medium as long as watering practices or rainfall do not compel the plant to tolerate wet feet. That would likely be the biggest obstacle to longevity. I have grown them in deep and shallow pots filled with gritty mix and 5:1:1 (not to be read they were mixed together). They CAN do equally well in either medium, but the gritty mix requires a closer eye on fertilizing regularly if you want the plants to get larger and have that 'glow' that comes with a high state of vitality. I find that extended dry periods cause the outer leaves to close up/inward, presumably to limit water loss. A nice rain or a splash with the hose quickly revitalizes the plants. They are about as bulletproof a plant as you'll find. Other than the tiny ones I enjoy growing in Chapstick caps or acorn caps, all the sempervivums I care for pretty much get watered only when it rains ..... or snows.

The Aeonium and Sempervivum are growing in Turface fines.

Al

Perhaps it would make more sense to zoom a bit farther out. Sempervivums, and nearly all succulents, are frequently classified as "summer-growers" or "winter-growers" or labeled as something that speaks to their "needs" based on what field experts have observed about them in the native habitat. But, fortunately for us hobbyists, we can greatly simplify many things into what we call "best practices," due to the fact that these highly specialized plants from the Swiss Alps are still just plants at the end of the day and behave in common, predictable ways when grown in cultivation.

Succulents are by and large opportunistic growers - sempervivums are an excellent example of this. If there is room* to grow, they will grow. If the harsh environmental conditions they have come to be adapted to are no longer the limiting factor in growth, they positively explode.

*Room, in this case, I am using as an umbrella term to refer to literal, physical space to expand, as well as the requisite temperatures, moisture content, nutrients, ability to perform gas exchange, etc.

When talking about the CEC, what we're actually discussing it seems, is the ability of a substrate to continue providing nutrients that are accessible to the plant, even in the absence of continued fertilization. The point is that the plants will not look like these glamour shot specimens you're referring to, Westes, if the limiting factor is a specific nutrient or a whole slew of nutrients.

For the matter of "clay loam" being the driving factor behind these specimens you see looking so magnificent, I find that doubtful. Reducing a well-rounded regimen of fertilization, watering, exposure to light, adequate watering, pest management, and god knows what else to "if I add 10% clay loam to this mix, I'll have similar looking plants," is... well it's just not good growing in my opinion. And it's poor advice to proliferate on a public forum that people of all levels of experience frequent.

There are basic tenets of growing that we can refer to and see proven right time and time again. We also have a responsibility to question those and scrutinize them extremely closely because the people who established any given "best practice" were just that: people, and inherently fallible.

That doesn't mean we have to be reductive in our side of the debate. Plants that are not given adequate nutrients to promote optimal growth will grow sub-optimally. There is no magic ingredient or ratio of a given material to put in a soil mix that will cause them to grow beyond their biological potential. We can only try to give them the conditions where they can achieve as close their potential as possible. If that means regular doses of liquid fertilizer when growing in a mostly inorganic mix, then that's what it means. If it means we adjust our soil mix to include higher organic materials (which has a much higher CEC than any form of clay at an average pH of 7) with an extra helping of some variety of clay and thus, forego the need to fertilize at every watering, then that's what it means.

@Indogulf BioAg LLC They don't need organic soil. But it was my observation that the published soil formulas by growers who specialize in Sempervivums do have small percentages of clay soil.